1. Field of the Invention
The present invention relates to moisture-activatable adhesives for medical application purposes. More particularly, the present invention relates to medical patches and transdermal therapeutic systems. The invention further comprises medical patches and transdermal therapeutic systems containing such moisture-activatable adhesives.
2. Description of the Prior Art
Medical patches and transdermal therapeutic systems (TTSs) generally possess a pressure-sensitive adhesive layer which enables self-adhesive attachment to the skin. In the case of transdermal therapeutic systems, the pressure-sensitive adhesive layer often also serves as an active substance reservoir, i.e. the pressure-sensitive adhesive contains one or more active substances which are delivered to the skin during the period of application.
In many cases, the pressure-sensitive adhesive layers of medical patches or of TTSs are made of polymers such as polyacrylates, polyisobutylenes, polyisoprenes or the like. A disadvantage of such pressure-sensitive adhesives, however, is that they adhere only poorly on a moist support. For this reason, when a patch or TTS is applied to a moist skin site the adhesion between the pressure-sensitive adhesive matrix layer of the patch or TTS and the skin may be insufficient. This problem exists in particular with patients who perspire vigorously, or with parts of the skin that show increased transpiration. Due to the insufficient adhesion, the patch or TTS may become detached entirely or partially so that the intended function can no longer be fulfilled. This may particularly affect the delivery of active substances from TTSs.
Because of the pressure-sensitive adhesive properties, that layer of a patch or TTS which is to be adhered to the skin has to be covered with a detachable protective film. Furthermore, some of the conventional pressure-sensitive adhesive compounds utilised for patches or TTSs have a strong tendency towards showing “cold flow”, which may lead to the adhesive compound emerging from the patch or TTS during storage, and subsequently causing the patch or TTS to stick to its pack. In addition, the conventional pressure-sensitive adhesive compounds are disadvantageous in that they are prepared almost exclusively with organic solvents, which may lead to problems due to the residual solvent content.
Furthermore, with active substance-containing adhesive matrix layers, it must be taken into account that at least for some active substances or active substance types an excessively lipophile environment can have a negative effect on the release of the active substances from the matrix. As a consequence, it is no longer possible to achieve the intended active substance release rate.